1. Field of the Invention
This invention relates to a pacing lead with sensor mounted therein for measuring the occurrence of a phenomenon in a living organism, and more particularly, to a pacing lead having a piezoelectric sensor, the pacing lead being implanted in a living organism whereby the phenomenon acting on the sensor will generate an electric waveform indicative of the phenomenon. The phenomenon sensed is typically contractions of the heart.
2. Description of the Prior Art
Heretofore, various sensors have been developed for sensing phenomena occurring in living organisms, and particularly, the human body and heart. For example, cardiac sensors are disclosed in U.S. Pat. Nos. 2,634,721; 3,038,465; 3,490,441; 3,811,427 and 3,831,588. These sensors have utilized various complicated constructions, such as strain gauges in U.S. Pat. Nos. 2,976,865 and 4,003,370, field effect transistors in U.S. Pat. No. 3,946,724, PN type transducers in U.S. Pat. No. 3,710,781, and signal generating semiconductor devices in U.S. Pat. No. 3,811,427.
Further, it has been experimentally suggested to use piezoelectric sensors for measuring heart beats and blood flow by wrapping a band of piezoelectric material around a patient's chest or leg, including those of the ferroelectric polymer and polyvinylidene fluoride (PVF.sub.2) types. For example, see "Ferroelectric Polymers and their Application" by Michael A. Marcus, appearing in Ferroelectrics: 40, 1982, and "Piezoelectric High Polymer Foils as Physiological Mechanic-Electric Energy Converters" by E. Hausler, H. Lang and F. J. Schreiner, appearing in IEEE 1980 Bio Medical Group Annual Conference, Frontiers of Engineering in Health Care.
Further, it is known to implant a piezoelectric device in a living organism for other purposes, such as to: power a cardiac or other pacer as suggested in U.S. Pat. No. 3,659,615, and control or vary the pacing rate with the implantee's own physical activity as disclosed in U.S. Pat. No. 4,140,132.
It has also been known that under controlled clinical conditions one can, by placing a microphone on the chest of a person, measure the vibrations of the heart and obtain graphs of waveforms showing, at a minimum, the opening and closing of the heart valves. See, for example, "The Analysis and Interpretation of the Vibrations of the Heart, as a Diagnostic Tool and Physiological Monitor" by C. M. Agress, M. D. and L. G. Fields appearing in IRE Transactions on Biomedical Electronics, July 1961.
As will be described in greater detail hereinafter, it has been found from studies on dogs using a pacing lead having a piezoelectric sensor mounted in the distal end portion thereof in accordance with the teachings of the present invention, that graphs of waveforms can be obtained clearly showing the opening and closing of the heart valves. This can be significant since from measurements of opening and closing of the heart valves, one can determine stroke volume and then by multiplying stroke volume by heart rate, one can determine cardiac output.